Impact mechanism for a repeatedly striking hand-held machine tool

ABSTRACT

A percussion mechanism for a repetitively hammering hand power tool, whose striking frequency and striking intensity are controllable independently of one another, has a striker ( 2 ), movable axially forward and backward in a guide barrel ( 1 ), and a device ( 5 ) exerting pressure on the striker ( 2 ), as a result of which the striker can be set into a forward motion in the direction of a tool bit ( 4 ) that is insertable into the hand power tool. A blocking element ( 10 ) is also provided, with which the striker ( 2 ) is blockable in its forward motion, and the striking frequency of the striker ( 2 ) is adjustable by controlling the blocking time of the blocking element ( 10 ).

PRIOR ART

The present invention relates to a percussion mechanism for arepetitively hammering hand power tool—preferably a drill hammer and/orpercussion hammer—that has a striker which can move axially forward andbackward in a guide barrel, and having a device that exerts pressure onthe striker, by which the striker can be set into a forward motion inthe direction of a tool bit that can be inserted into the hand powertool.

One such compression percussion mechanism that executes repetitivestriking motions for an electropneumatic drill hammer and/or percussionhammer, as is taught by German Patent DE 198 10 088 C1, comprises aneccentric drive, a piston, and a striker. With these three elements, arotary motion is converted into a reciprocating motion. The axialforward and backward motion of the striker in a guide barrel happens inthe following way:

The piston moved in the forward direction by the eccentric drivecompresses the air cushion between the piston and the striker, causingthe striker to shoot freely onto the tool bit inserted into the powertool. The striker transfers its percussion energy to the tool bit andthere receives a pulse in the reverse direction. Simultaneously, thepiston is likewise moved backward by the eccentric drive, creating acertain underpressure in the air cushion between the piston and thestriker. As soon as the piston has reached its turning point and thestriker shoots still farther against the piston, the air cushion betweenthe two is compressed, resulting in compression, with the consequencethat upon the next forward motion of the piston, the striker shootsforward against the tool bit at an even higher speed.

A compression percussion mechanism of this kind is technicallyrelatively complex, since besides the striker that moves in the axialdirection it requires an eccentric drive with a piston that is likewisedisplaceable in the axial direction. A mutually independent adjustmentof the striking frequency and the striking intensity is not possible ina compression percussion mechanism of this kind.

It is therefore the object of the invention to disclose a percussionmechanism of the type defined at the outset which can be implementedwith the simplest possible technical means.

ADVANTAGES OF THE INVENTION

The stated object is attained with the characteristics of claim 1 inthat there is a device that exerts pressure on the striker, as a resultof which the striker can be set into a forward motion in the directionof a tool bit that can be inserted into the hand power tool, and that ablocking element is provided, with which the striker can be blocked inits forward motion, and the striking frequency of the striker can beadjusted by controlling the blocking time of the blocking element.

The percussion mechanism according to the invention requires few movingmechanical parts and is therefore less subject to wear. Moreover, thispercussion mechanism, which unlike conventional compression percussionmechanisms has no eccentric drive and no piston, makes a compact designpossible. Furthermore, the striking frequency of the percussionmechanism and the striking intensity can be controlled independently ofone another.

Advantageous embodiments of the invention are disclosed by the dependentclaims.

Advantageously, the device exerting pressure on the striker comprises apressure reservoir that is can be filled with a gas and that is locatedon the side of the striker diametrically opposite the tool bit. Thegas—preferably air—can be delivered to the pressure reservoir via aninlet valve, and the quantity of gas delivered, and thus the pressureexerted on the striker, are controllable. For delivering gas to thepressure reservoir, a pump device may be provided, which is located forinstance in the hand power tool.

It is expedient that the pump device is located in the hand power tool.

Advantageously, the blocking time of the blocking element can becontrolled as a function of a fixedly predetermined or user-controllablyselectable striking frequency and/or as a function of the pressure levelin the pressure reservoir.

DRAWINGS

The invention is described in further detail below in terms of anexemplary embodiment shown in the drawing.

Shown are:

FIG. 1, a longitudinal section through a drill hammer and/or percussionhammer with a percussion mechanism; and

FIG. 2, a detail of the percussion mechanism with control for thestriker.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

In FIG. 1, a drill hammer and/or percussion hammer is shown inlongitudinal section, as an example of a repetitively hammering handpower tool; FIG. 1 is essentially limited to those parts that belong tothe percussion mechanism of the drill hammer and/or percussion hammer.

The drill hammer and/or percussion hammer has a guide barrel 1, in whicha striker 2 is supported, movably axially forward and backward. Theguide barrel 1 is adjoined by a tool bit holder 3, in which a tool bit4, such as a drill or chisel, is inserted, likewise movable withincertain limits in the axial direction. In the guide barrel 1, on thebackside of the striker 2, which is the side of the striker 2diametrically opposite the tool bit 4, there is a pressure reservoir 5filled with a gas—preferably air. This pressure reservoir 5 is filledwith gas via an inlet valve 6 by a pump device 7.

In the exemplary embodiment shown, the pump device 7 is located in thehand power tool itself. However, the pump device 7 may also be locatedoutside the hand power tool and may communicate with the inlet valve 6via a pressure line. The quantity of the gas delivered to the pressurereservoir 5 from the pump device 7 may be controlled via the inlet valve6, which is for instance an electrically controllable valve. Thepressure exerted on the striker 2 and thus the striking intensityexerted by the striker 2 on the tool bit 4 depends on the quantity ofgas delivered to the pressure reservoir 5. In other words, the strikingintensity of the drill hammer and/or percussion hammer can be controlledvia the quantity of gas delivered to the pressure reservoir 5. In thepressure reservoir 5, it is expedient to provide an outlet valve 8 whichlimits the gas pressure in the pressure reservoir 5 to a predeterminablemaximum value.

In the view shown in FIG. 1, the striker 2 is located in an outsetposition, in which it closes a gas outlet opening 9 located in the guidebarrel 1. In this outset position, the striker 2 is restrained by ablocking element 10. The blocking element 10, in a very simpleembodiment, is for instance a bolt, which can penetrate through anopening 11 in the side wall of the guide barrel 1 into an indentation 12in the striker 2. If the blocking element 10 is now pulled out of theindentation 12 in the striker 2, the striker 2, because of the gaspressure in the pressure reservoir 5, shoots in the forward directiontoward the tool bit 4 and simultaneously uncovers the gas outlet opening9 in the guide barrel 1. Thus while the striker 2 is shooting at thetool bit 4 and imparting its percussion impetus to the tool bit 4, thegas pressure is discharged through the gas outlet opening 9 on thebackside of the striker 2 facing toward the pressure reservoir 6.

The reverse percussion impetus at the tool bit 4 causes the striker 2 tomove in the reverse direction toward the pressure reservoir 5 and tore-close the gas outlet opening 9. The rearward motion of the striker 2can also be reinforced by a compression spring 13, located on the frontside oriented toward the tool bit 4, or by a similarly acting mechanical(for instance pneumatic) or electrically acting device. Once the striker2, after its rearward motion, has regained its outset position in thisway, it is blocked by the blocking element 10, which again penetratesinto the indentation 12 in the striker 2. If the blocking element 10 ispulled out of the indentation 12 of the striker 2 again, then thestriker 2 executes a new forward motion and in the process exerts afurther impact on the tool bit 4. It can be seen that the strikingfrequency of the striker 2 is controllable solely by the length of theblocking time of the blocking element 10.

In conjunction with FIG. 2, one possible version of control of theblocking element 10 will now be described in further detail. This viewshows a detail of the striker 2 with the blocking element 10 and withthe device for controlling for a blocking element 10.

The control of the blocking element into a locking or unlocking positioncan be done for instance on the principle of an electromagnet. Theblocking element 10 then forms a core of ferromagnetic material of acoil 14 to which current can be supplied. The coil 14 is located in adome 15 placed on the guide barrel 1 over its opening 1 1. When currentis supplied to the coil 14, the blocking element 10 is pulled into thedome 15 by electromagnetic forces, causing the blocking element 10 tomove out of the indentation 12 in the striker 2 and to unblock thestriker 2. As soon as the flow of current through the coil 14 isinterrupted, a spring 16 located in the dome presses the blockingelement 10 back through the opening 11 in the guide barrel 1 onto thestriker 2. If the striker 2 is moving rearward and its indentation 12reaches the location of the blocking element 10, then the blockingelement 10 automatically slides into the indentation 12 because of thespring force 16 and blocks the striker 2 in its outset position.

The current flow through the coil 14 and thus the blocking time of theblocking element 10 are controlled by a control unit 17. Final controlelements for the control unit 17 may for instance be an actuator 18,actuatable by the user of the hand power tool, for the strikingfrequency, or a pressure sensor 19, which detects the gas pressure inthe pressure reservoir 5. It is thus possible to control the blockingtime of the blocking element 10 as a function of a user-selectablestriking frequency and/or as a function of the pressure level in thepressure reservoir 5. However, equally well, a fixed striking frequencycan be predetermined for the control unit 17, which controls the currentflow through the coil 14 accordingly. The control unit 17 may, however,also be supplied with still other controlling variables for the strikingfrequency.

The control unit 17 may furthermore be used to control the gas pressurein the pressure reservoir 5 via the electrically controllable inletvalve 6. The striking intensity can thus be controlled. For thatpurpose, a further final control element 20, actuatable by the user ofthe hand power tool, should be provided.

1. A percussion mechanism for a repetitively hammering hand power tool—preferably a drill hammer and/or percussion hammer—that has a striker (2), movable axially forward and backward in a guide barrel (1), having a device (5) that exerts pressure on the striker (2), by which the striker (2) is capable of being set into a forward motion in the direction of a tool bit (4) that is insertable into the hand power tool, characterized in that a blocking element (10) is provided, with which the striker (2) is blockable in its forward motion; and that the striking frequency of the striker (2) is adjustable by controlling the blocking time of the blocking element (2).
 2. The percussion mechanism in accordance with claim 1, characterized in that the device exerting pressure on the striker (2) comprises a pressure reservoir (5) that is fillable with a gas and that is located on the side of the striker (2) diametrically opposite the tool bit (4).
 3. The percussion mechanism in accordance with claim 2, characterized in that the gas—preferably air—is deliverable to the pressure reservoir (5) via an inlet valve (6).
 4. The percussion mechanism in accordance with claim 3, characterized in that the quantity of the delivered gas and thus the pressure exerted on the striker (2) are controllable.
 5. The percussion mechanism in accordance with claim 3, characterized in that a pump device (7) is provided, which delivers the gas to the pressure reservoir (5).
 6. The percussion mechanism in accordance with claim 5, characterized in that the pump device (7) is located in the hand power tool.
 7. The percussion mechanism in accordance with claim 1, characterized in that the pressure reservoir (5) has an outlet valve (8), which limits the gas pressure to a predeterminable maximum value.
 8. The percussion mechanism in accordance with claim 1, characterized in that the blocking time of the blocking element (10) is controllable as a function of a fixedly predetermined or user-selectable striking frequency and/or as a function of the pressure level in the pressure reservoir (5). 